1. Field of the Invention
The present invention generally relates to signal communications, and more particularly, to an architecture for protecting electronic circuitry used for communications between a frequency translation apparatus, which may be referred to herein as a frequency translation module (FTM), and an integrated receiver-decoder (IRD) or between a low noise block (LNB) and an IRD from voltage surge.
2. Background Information
In a satellite broadcast system, one or more satellites receive signals including audio and/or video signals from one or more earth-based transmitters. The satellite(s) amplify and rebroadcast these signals to signal receiving equipment at the dwellings of consumers via transponders that operate at specified frequencies and have prescribed bandwidths. Such a system includes an uplink transmitting portion (i.e., earth to satellite(s)), an earth-orbiting satellite receiving and transmitting portion, and a downlink portion (i.e., satellite(s) to earth).
In dwellings that receive signals from a satellite broadcast system, signal receiving equipment may be used to frequency shift the entire broadcast spectrum of the satellite(s), and frequency stack the resultant output onto a single coaxial cable. However, as the number of satellites within a satellite broadcast system increases, and with the proliferation of high definition satellite channels, a point will be reached where the total bandwidth required to accommodate all of the satellites will exceed the transmission capability of the coaxial cable. It has become necessary for the satellite decoder industry to implement more satellite slots into their distribution systems. To provide for the increased number of satellite slot transmissions a more elaborate means for satellite configurations selection is required. The two primary methods, used now for selecting these various configurations are the legacy LNB power supply method and the new Frequency Translation Module (FTM) method.
The legacy LNB power supply method controls satellite RF tone on or off selection by voltage level and a superimposed, 600 mvp-p, 22 kHz tone. Tone selection is accomplished by either a constant tone or a Pulse Width Modulated (PWM) tone. The industry standard for the PWM tone is called DiSEqC and is defined in the Eutelsat DiSEqC Bus Functional Specification. The two stage, output voltage (13 or 18 volts) is typically used to select the polarity of incoming satellite signals and the tone selects various satellite slots in space.
The second method (FTM) is self powered, therefore, it does not require an LNB power supply, and uses a UART controlled 2.3 MHz, Frequency Shift Key (FSK) modulation scheme to communicate selection commands to the satellite configuration switch. Other modulation methods may be substituted for the UART modulation method. The FTM switch is designed to select a satellite signal transponder from a host of satellite receiver antennas and translate it, in frequency, to a single transponder. This new frequency shifted transponder band is then sent to the satellite decoder box through the connecting coax cable.
Present day satellite decoder systems need the ability to switch between these two communication methods and operate in either mode without being disturbed by the other system. If a satellite receiver system is capable of FTM operation, the conventional LNB power supply will be disabled such that all control and selection of the available satellite signals is done with the modulated 2.3 MHz, FTM communication channel. However, a problem presented by this multiband configuration is the inability of conventional lighting surge protection circuits to coexisting with the DC voltage and 22 kHz DiSEqC signal as well as the high amplitude 2.3 MHz FTM carrier signal and 900 MHz broadcast satellite signals without distorting any of these waveforms. Previous single transient voltage suppression diode protection scheme, used in legacy Set Top Boxes, distort the 2.3 MHz signal by becoming forward biased during portions of the 2.3 MHz wave period.
Furthermore, the absence of the LNB DC supply voltage on the transmission line reduced the amount of negative voltage required to forward bias protection diode. Under these previous conditions, the FTM signal could forward bias the protection diode when the 2.3 MHz signal is in its negative phase. There exists a need for a FTM and IRD protection circuit that can protect the circuitry from voltage and current surge without distorting the waveforms transmitted on the transmission line. The present invention described herein addresses this and/or other problems.